Technical Field of the Invention
The present invention relates to a control unit for robots, and in particular, to a control unit for controlling speeds of industrial robots.
Related Art
As is well known, in a robot, a speed command is outputted from a control circuit and a motor is activated so as to follow the speed command (e.g., see JP-A-2012-223881). During an acceleration period in which the motor is accelerated, the actual speed of the motor is usually slightly different from the speed command value. That is, the actual speed is usually lower than the speed command value. This is attributed to the fact that electric power sufficient for meeting required torque is not supplied during the acceleration period, in spite of the fact that the required torque is increasing in the acceleration period. As a measure against this, a drive power circuit that supplies electric power for driving the motor may be designed such that the torque required in the acceleration period is constantly met. Such a design of the drive power circuit may lessen the difference of the actual speed of the motor from a speed command value to thereby enhance the follow-up performance of the motor.
However, when the drive power circuit is designed with reference to maximum torque required during the acceleration period, the power capacity of the circuit is required to be increased. Therefore, the size of circuit parts to be used is increased and accordingly the size of the control unit is increased. Further, when the power capacity is increased, power consumption of the driver power circuit itself is also increased. In practice, however, large torque is particularly required only in the acceleration period. In addition, in terms of a practical control cycle of a motor, the proportion of the acceleration period is comparatively small. When these matters are taken into account, designing a drive power circuit with reference to maximum torque may create a power-excessive state in most of the operation period of the robot including a suspension period when the motor is not driven, but for the acceleration period. At the same time, the increase in power consumption of the drive power circuit may constantly allow unnecessary power consumption (power loss). For these reasons, as it now stands, the departure of the actual speed of a motor from a speed command is tolerated because the departure raises no serious problem in terms of the specification of the robot. However, the follow-up performance of a motor is desired to be enhanced by reducing the difference of the actual speed of a motor from a speed command value. On the other hand, the size of the control unit and the occurrence of power loss are also desired to be reduced. In the conventional art, it is difficult to balance the enhancement of the follow-up performance of a motor, with the reduction in the size of the control unit and in the occurrence of power loss.